Effect of Seasonal Temperature Changes on Thyroid Structure and Hormones Secretion of White Grouper (Epinephelus Aeneus) in Suez Gulf, Egypt

The thyroid is the largest and one of the phylogenetically oldest endocrine glands in vertebrate species. It is the first endocrine structure to become recognizable during an animal's development. Although the thyroid gland is structurally conserved in all vertebrate species, exhibiting a similar follicular structure and function. Seasonal temperature changes on the thyroid gland structure and hormones secretion was examined in white grouper; Epinephelus aeneus in Seuz Gulf, Egypt. 60 male of white grouper; E. aeneus (138.5 +/- 6.05 g) were netted from Suez Gulf during a year from July 2008 to June 2009. Water temperature and salinity were ranging from 12 to 34 degrees C and 39 to 40 ppt during cold and warm seasons, respectively. Blood samples were collected from the caudal vein for thyroid hormones analysis. Samples of E. aeneus were dissected to expose the internal organs, histological examination and measuring the cell height of the thyroid epithelium. Thyroid gland composed of follicles scattered around the ventral aorta, near the gills. Follicular cells varied according to secretion of the gland during warm and cold seasons. Thyroid hormones [Triidothyronine (T-3) and Thyroxin (T-4)] were detected in the fish serum in levels ranged from 1.28-4.08 ng/ml for T-3 and 0.22-1.11 ng/ml for (T-4) in the warm and cold seasons, respectively. The results showed that the height of thyroid epithelium and plasma concentration of thyroid hormones (thyroid activity) in Epinephelus aeneus increased significantly during spring and summer. The peak of these factors occurred in midsummer (August). Then, the thyroid activity decreased significantly during autumn and early winter from October to December according to the decreasing of temperature. T-3 and T-4 increased significantly from January to April. [Hossam H. Abbas, Mohammed M. Authman Mona S. Zaki and Gamal F. Mohamed. Effect of Seasonal Temperature Changes on Thyroid Structure and Hormones Secretion of White Grouper (Epinephelus Aeneus) in Suez Gulf, Egypt. Life Sci J 2012; 9(2): 700-705]. (ISSN: 1097-8135). http://www.lifesciencesite.com. 105